1. Field of the Invention
The present invention relates to an automatic lathe, and, more particularly, to an automatic lathe which has a pair of gang tool posts (comb-shaped tool posts) disposed on respective sides of a headstock to be independently movable in two perpendicular directions, thereby shortening the machining time to eventually improve the productivity.
This invention also relates to an automatic lathe which has a pair of gang tool posts disposed on respective sides of a headstock to be independently movable in two perpendicular directions, with specially designed pitches between a plurality of work tools attached to each gang tool post.
Further, this invention relates to an automatic lathe which has a pair of gang tool posts disposed on respective sides of a headstock to be independently movable in two perpendicular directions, with an improved attachment structure for rear work tools.
2. Description of the Related Art
One example of an automatic lathe is designed as follows. This automatic lathe has a headstock which is designed movable in the direction of a Z axis parallel to the axial direction of a main spindle. A pair of gang tool posts are disposed in front of the headstock and on both sides (e.g., right and left sides) thereof, respectively. The gang tool posts are designed to be movable in the directions of an X axis and Y axis perpendicular to the Z-axial direction. The controls of the gang tool posts in the X-axial direction and Y-axial direction are not performed independently. For example, both gang tool posts make the same movement in the X-axial direction. In the Y-axial direction, the gang tool posts can make the same movement or one gang tool post moves forwardly in the Y-axial direction (upward) while the other gang tool post moves reversely in the Y-axial direction (downward) because both gang tool posts are coupled by a rack and pinion mechanism.
According to the above conventional structure, however, as a pair of gang tool posts make movements mutually associated with each other, both gang tool posts cannot be used simultaneously to machine workpieces, or their usage is limited so that while one is used to machine a workpiece, the other cannot be ready for the next machining (to wait near the workpiece). Therefore, only one gang tool post is used to sequentially machine workpieces, requiring a longer machining time. This inevitably reduces the productivity.
A structure for mounting a plurality of work tools on a pair of gang tool posts will be discussed below. Those work tools are arranged in alignment at given pitches, with their free ends aligned in a line. In machining a workpiece, there may be a case where the pair of gang tool posts are moved to cause the free end of one of the work tools mounted on each gang tool post to contact the outer surface of the workpiece, and machining, such as turning or boring, is then carried out with the two work tools brought at the respective sides of the workpiece.
To attach the work tools to each gang tool post, the work tools are positioned one by one and are then secured by attaching members. In actual attachment, however, an attachment error is likely to occur so that the free ends of all the work tools are not precisely aligned in a line. That is, the free ends of some work tools may have variations in a direction toward and away from the opposite gang tool post.
Some workpieces, which are to be subjected to turning, may have a very small outside diameter, and if the outside diameter is close to the mentioned attachment error of the work tools, the following problem may arise. Because the pitches between the work tools are constant, as the free ends of predetermined two work tools come close to each other at the time those two work tools are positioned at predetermined positions, the free ends of the other work tools also come close to those of the opposite work tools. At this time, if there are any opposite work tools each standing out more than the other on the same side due to the aforementioned attachment error, the free ends of such two work tools may abut on each other, the abutting work tools may have nicked blades or edges or the work tools may not perform proper machining.
There may be another case where a plurality of front work tools are mounted on a rear headstock in an automatic lathe with a plurality of rear work tools secured to the lathe body, so that the front work tools will machine the front side of a workpiece held on a main headstock while the rear work tools machine the rear side of a workpiece held on the rear headstock. In this case, the front work tools and the rear work tools should keep a predetermined size relation, thus requiring high level of parts and assembly accuracy or a separate expensive positioning mechanism.
This problem will be described below specifically with reference to FIG. 19. One of front work tools 315a, 315b and 315c bores a hole in the front face of a workpiece 311 held on a main spindle 303 while one of rear work tools 317a, 317b and 317c bores a hole in the back face of a workpiece 311a held on a rear spindle 307. In this case, first, a rear headstock 305 is moved in the X-axial direction to align the front work tool 315a with the center line of the main spindle 303 and align the center line of the rear spindle 307 with the rear work tool 317a. Under this situation, the headstock is moved in the Z-axial direction and the rear headstock 305 is moved in the Z.sub.1 -axial direction. Accordingly, the work tool 315a bores a hole in the front face of the workpiece 311 held on the main spindle 303 while the rear work tool 317a bores a hole in the back face of the workpiece 311a held on the rear spindle 307.
The same is true of the case where the front work tool 315b and rear work tool 317b are used to simultaneously machine the front face of one workpiece and the back face of another workpiece, respectively, and the case where the front work tool 315c and rear work tool 317c are used for similar simultaneous machining of the front and back faces of the respective workpieces.
To perform the aforementioned simultaneous machining, however, the interval (a.sub.1) between the center of the rear spindle 307 and the front work tool 315a, the mutual intervals (b.sub.1) and (c.sub.1) between the front work tools 315a, 315b and 315c, the interval (a.sub.2) between the center of the main spindle 303 and the rear work tool 317a, and the mutual intervals (b.sub.2) and (c.sub.2) between the rear work tools 317a, 317b and 317c should satisfy relations given by the following equations (I), (II) and (III). EQU a.sub.1 =a.sub.2 (I) EQU b.sub.1 =b.sub.2 (II) EQU c.sub.1 =c.sub.2 (III)
To obtain the relative positional relations expressed by the above equations (I) to (III), a positioning mechanism should be provided on the side of the rear work tools 317a, 317b and 317c, for example, or high level of parts and assembly accuracy is required if such a positioning mechanism is not provided. Both cases will result in an increased cost performance.
It is also necessary to respectively align the axial centers of the front work tools 315a, 315b and 315c with those of the rear work tools 317a, 317b and 317c in the vertical direction. This also requires a positioning mechanism or high level of parts and assembly accuracy, which will raise a similar problem on the cost performance.